Chemically resistant structure



Aug. 1,

H. H. HARKlNs 2,167,716

CHEMICALLY RESISTANT STRUCTURE Filed Oct. 12, 1955 BW* f" ATTORNEY.

r are objectionable because attacked atented Aug. 1, 1939 PATT Gi'FiCECHEMICALLY nEsIsTANr s'rnoc L 1 Henry Harvey Harkins,

River Edge, N. J., assimilor, by mesne assignments, to lUnited StatesRubber Company, New York, N. if., a corporation ci New JerseyApplication October l2, i935, Seriallblo. dhtdfl 3 Claims.

This invention relates to improvements in chemically resistantstructures and more particularly to Wall structures bearing rubbercoatings or linings whereby to improve their resistance lto fractureunder widely varying temperature conditions.

I Rubber coatings are desirable for the protection of various containersfor the storage, transportation and utilization of corrosive or otherliquids for example, acids, alkalis, salt solutions, etc. and amongwhich are storage tanks, pickling tanks, electroplating tanks, railwaytank cars and the like.

Soit rubber coatings or linings, that is, coatings containing up to 4-5%of combined sulphur, easily by many corrosive liquids and organicsolvents and because easily cuter torn. Hard rubber coatings or linings,that is, rubberl coatings which have a chemically-combined sulphurcontent of 30% or more, due to the wide difference between theirthermal'expansion co-efcients and that of the wall, usually metal, towhich it is bonded, tend to become cracked when subjected to widelyvarying temperature conditions. Such linings are particularly liable tofailure at very low temperatures, e. g.`, 0 to 40 C.

lt has also been proposed to line containers with separate overlappingsheets of hard rubber, with a cushion layer of soft, resilient rubberintervening between the hard rubber sheets and the metal wall to absorbthe greater relative expansion and contraction of the hard rubber, thelap seams acting as expansion joints. In such a construction, however,the hard rubber has been found to have a much lower impact strength thanwhen it is adhered directly to the metal wall, This is because the soft,resilient cushion layer yields readily and permits excessive localstrain and consequent fracture of lthe hard rubber layer when the latteris subjected to a heavy impact. ln commercial practice the impactweakness inherent in such construction has been partially overcome byapplying over the hard rubber a protective layer of soit rubber, thussacriiicing, however, the advantage of chemical inertness inherent inthe use of hard rubber as the outer layer. Such three-layer linings havebeen found to be fairly satisfactory, from the point 0i View of impact(oi. isiiti resistance, for containers situated indoors or where theprevailing temperatures remain well above freezing temperatures. But atvery low temperatures, even though the soft rubber of the cushion layerand the expansion joints con- 5 tinues to function satisfactorily asregards the absorption of stresses due to contraction, the extremebrittleness of the hard rubber at very low temperatures, coupled withthe yielding nature of the soft cushion layer, results in very lowimpact strength. Thus it is seen that rubber lining constructionsheretofore proposed leave much to be desired.

An object of this invention is to provide a wall structure whereby toovercome the above disadvantages, and provide one having a high iml5pact strength at all temperatures and substantial freedom from crackingand buckling due to wide temperature changes. Other objects will beapparent from the following description.

Accordingly. the invention comprises interposing between the supportingwall base and a hard rubber sheet or coating, a supporting layertherefor of a rubber or rubber-like material, characterized by ahardness and non-resiliency approaching that of ebonite but having arela- 'tively low modulus oi rigidity approaching that of soft rubber.Typical oi such an intermediate material is so-called semi-hard rubberwhich may be obtained by vulcanizing a rubber compo-I sition to achemically-combined sulfur content intermediate between that of softrubber and that of hard rubber or ebonite, for example achemically-combined sulfur content of from about l2 to about 2bn/.3 byweight 'based on the rubber content, i. e. coefticient of vulcanization30 of from about l2 to about 2li.,

Such semi-hard rubber has at ordinary' temperatures a inoduius oirigidity on the order oi llll to lilllil pounds per square inch, ascompared with a value on the order oi Zllpounds per square inch for softrubber and a value on the order oi iililildil to 200ml@ pounds persuuareinch for hard rubber. By virtue oi" the relatively low modulus ofrigidity oi Ithe semi-hard 5 rubber employed in the invention as thesupporting layer for the rubber sheets, the vslipporting layer iscapable oi 'undergoing sufricient shearing deformation, in directionsparallel to the wall surface, to compensate tor the differences inthermal expansion and contraction of the outer hard rubber sheets andthe metal wall. fracture and separation of the sheets when subjected towidetemperature changes.

Another property of such semi-hard rubber is its ultimate elongationunder tensile stress, which is closely related to the modulus ofrigidity and may accordingly be used to characterize the material. Theultimate elongation at ordinary temperatures is on the order of 100% ofthe initial length, as compared with values on the order of 1000% forsoft rubber and on the order of 2% to 10% for hard rubber.

By virtue of the hardness and non-resilience of the semi-hard supportinglayer, in which properties it is comparable to hard rubber, the hardrubber of my lining structure is not substantially deflected whensubjected to heavy impacts and is therefore highly resistant to fractureunder such conditions. Furthermore, when the lining is subjected toextremely low temperatures the increase in hardness and brittleness ofthe hard rubber are paralleled by a corresponding increase in thehardness of the semi-hard rubber supporting layer, so that thecharacteristic high impact resistance is `preserved even at extreme lowtemperatures. A

A convenient method of constructing the lining is to ply togetherunvulcanized sheets of semihard rubber and hard rubber compounds. The'plied sheets are then secured to the cleaned, preferably sand-blastedmetal wall of the container' in known manner by means of a suitablerubberto-metal adhesive composition, as shown by Fig. l. The edges ofthe overlapping sheets are preferably over-skived. The rubber is thenvulcanized in place, by filling the container with hot water, or bysteam.

If desired, the lining construction may include as' shown by Fig. 2, anouterprotective layer of soft rubber over the hard rubber' sheets, themechanical advantages of the underlying structure being wholly retainedin such case.

'Ihe following table illustrates the superior impact resistance of thelining construction of the present invention. 'I'he test specimens wereprepared by interposing in construction A, a sheet of semi-hard rubbercomposition having a thickness of inch, between a cleaned metal plateand a sheet of hard rubber composition of a .thickness of V8 inch,adhesive being applied to the metal surface. In construction B, a softrubber composition of the same thickness, was substituted for thesemi-hard rubber composition. The laminated specimens were thenvulcanized, and were tested for impact strength on a Tinius- Olsenimpact machine (guillotine type), at various temperatures. In the tablewhich shows the results of the tests, the iigures given under the columnheading Height express the distances through which a tive-pound weightfell upon a chisel resting on the hard rubber face or the specimen.

The structure is thus capable of resistingl Type of construction Temp.Eilect None` Cracked. None. Cracked. None. Cracked. None. Cracked.

None indicates that the hard rubber did not crack under the impact.

Other materials having similar physical properties may be employed asthe supporting layer in place of the semi-hard rubber, the essentialcharacteristics being a modulus of rigidity on the order of 100 to 1000pounds per square inch, or an ultimate elongation on the order f 100%,and a hardness approaching vthat of hard rubber. Such materials whichare to be considered equivalents within the scope of this invention areexemplied by hard rubber which has been made ilexible and moreextensible by the incorporation in the mix, prior to vulcanization, ofiluxing agents which resemble soft rubber but which cannot be vulcanizedto a state resembling that of hard rubber, such as polymerizedchloroprene (2-chloro-butadiene-1,3), and the plastic, elastic reactionproducts as disclosed in United States Patents Nos. 2,016,026 and2,016,027, issued October l, 1935, and the like.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A chemically resistant construction comprising a supporting Walll anda lining of hard rubber separated therefrom by an intermediate bondingand shock absorbing layer of rubber material containing from abouttwelve to about twenty percent by weight of sulphur based on the rubbercontent, substantially all of the sulphur of said intermediate layerbeing chemically combined with the rubber portion.-

2. A chemically resistant construction comprisi'ng a supporting wall,and a lining of hard rubber containing at least 30 percent by weightbased on the rubber of chemically-combined sulphur, separated therefromby an intermediate bonding and shock absorbing layer of rubber materialhaving a sulphur content 'of from twelve to twenty percent by weightbased on the rubber content, substantially all of the sulphur of saidintermediate layer being chemically combined with the rubber portion. i

3. A chemically resistant construction comprising a supporting wall anda lining of hard rubber separated therefrom by an intermediate bondingand shock absorbing layer of rubber-containing material having ahardness and a modulus of rigidity substantially the same as vulcanizedrubber having a coeillcient of vulcanization of from about 12 to about20.

